Phosphorylase kinase (PhK) is a multi-subunit enzyme primarily expressed in liver and skeletal muscle, where it functions to couple glyconeolysis to hormonal stimuli. Several human metabolic disorders, known collectively as the glycogen storage diseases VIII, result from a deficiency in either the skeletal muscle or liver form of PhK. A model system for the skeletal muscle PhK deficiency is the I/Lyn mouse strain in which a mutation on the x-chromosome results in a PhK deficiency in only the adult skeletal muscle enzyme. Both the liver and neonatal skeletal muscle have normal enzyme activity. We will investigate the molecular basis for the I/Lyn defect and the mechanisms which regulate the tissue-specific and developmental expression of PhK by using recombinant DNA techniques. A procedure is proposed to develop a cDNA probe which is complementary to the mRNA for the PhK catalytic subunit Gamma, which is known to be absent in the I/Lyn skeletal muscle. The cDNA probe will be used for northern analysis to determine whether particular Gamma-mRNA species are expressed in the various normal tissues and to determine if there is switching from a neonatal to an adult message during muscle development. By comparing these results with a similar analysis of the I/Lyn tissues it can be determined if a particular Gamma-mRNA species is absent or altered in the I/Lyn skeletal muscle. The cDNA probe also will be used to examine the structure of the Gamma-gene in the normal and I/Lyn mice by Southern analysis. This analysis will determine whether there are multiple Gamma-genes from which the different Gamma-mRNAs are transcribed or whether there is a single gene transcribed by different mechanisms. Furthermore, the comparison of the normal and I/Lyn Gamma-genes may indicate what alterations are present in the I/Lyn Gamma-gene to account for the absence of the Gamma-subunit. The results of this investigation will define the mechanisms which regulate the tissue-specific and developmental expression of the Gamma-subunit and contribute to our understanding of a genetic metabolic disorder.